1. Field of the Invention
The invention relates in general to load fixtures for industrial furnaces, and more specifically to load fixtures having a multi-tier assembly that is insertable into a top-loading furnace.
2. Description of the Prior Art
Top-loading high-temperature furnaces are used in industrial applications for the heat treatment and the sintering of small articles. These furnaces are typically useful in a research and development laboratory, a quality assurance station, or production line. The articles to be treated are often a group of small objects or work pieces and thus are collectively known as a load. These furnaces are equipped to subject a load to a temperature in the range of 1700 degrees centigrade and to a sealed gaseous or evacuated environment. The furnace chamber, wherein the load is placed, is completely enclosed and usually accessable only by a hinged or removable door at the top of the furnace.
In such furnaces as described above a tray or a basket is sometimes used as a stable platform for placing a load within the chamber. However, a more versatile fixture is required that can accommodate a variety of large and small loads and that can subject the load articles to effective heat treatment regardless of their number or size. The relative positions of articles will affect the heat treatment they receive; moreover, a small load mass relative to a large fixture mass will also degrade the heat treatment. Therefore, a need exists for a fixture that is large enough to carry a maximum load yet is adaptable to a small load.
Further, there exists a need to ascertain the temperatures of various levels within the furnace chamber while it is in operation, and to monitor the temperature of the radial thermocouple that is traditionally used for feedback control of the furnace heating elements. More specifically, it is necessary to obtain independent optical pyrometer measurements of the ambient temperature in the vicinity of the load while the furnace is closed and operating. Typical top-loading furnaces include a viewport in the center of the access door. Because the aperture of the optical path into the chamber is quite small (typically 0.76 centimeters in diameter), any object monitored by a pyrometer must be accurately aligned with the optical path.
The placement of a load in the chamber is difficult. In the prior art, a load is typically lowered by hand onto a hearth plate or, alternatively, the load is distributed upon a basket or tray which is inserted by hand into the furnace. A typical top-loading furnace chamber is tall and narrow with its top opening is being about 15 centimeters in diameter. Thus, when the furnace is loaded, the user's hand obscures all view of the load, the carrier when used, and the interior of the chamber. Normally, considerable trial and error is required involving the repeated opening and closing of the furnace and repositioning of the load, before adequate alignment is achieved.